Surgical Model for Analysis of Signal Transfer Through Biologic and Synthetic Materials.

BACKGROUND: High-fidelity volitional control of bioengineered prosthetic limbs with multiple degrees of freedom requires the implantation of multiple recording interfaces to detect independent control signals. However, interface utilization is complicated by interfering electrophysiological signals originating from surrounding muscles and nerves, leading to equivocal signal detection. We developed and validated a surgical model to characterize signal propagation through various biomaterials to identify insulating substrates for use in implantable interfaces. The identification of these insulating materials will facilitate the acquisition of noncontaminated prosthetic control signals, thus improving manipulation of advanced prosthetic limbs. METHODS: Using a rat hindlimb model, 4 groups (n = 8/group) were tested. A medial gastrocnemius muscle flap was elevated, leaving the neurovascular pedicle intact. The flap was rotated into a chamber and secured to a silicone base. A stainless steel electrode was affixed to the surface of a muscle and encircled by 1-layer small intestinal submucosa (SIS), 4-layer SIS, silicone elastomer, or nothing (uninsulated). A superimposing electrode was attached, and an external silicone layer was wrapped around the construct and sutured in place. Electromyographic studies were then performed. RESULTS: This model was found to correspond with expected signal isolation characteristics of the nonconductive silicone group, electrically inert single and multilayer SIS group, and the uninsulated group. Signal isolation of compound muscle action potential amplitude at stimulation threshold was significantly greater using silicone (51.4%) compared with the 1-layer SIS (-6.8%), 4-layer SIS (-3.3% ), or uninsulated groups (1.2%) (P = <0.001). Isolation of the maximum compound muscle action potential peak-to-peak amplitude was also greater with silicone (56.7%) versus the 1-layer SIS (1.5%), 4-layer SIS (1.1%), or uninsulated groups (-0.7%) (P = <0.001). CONCLUSIONS: This study demonstrates and validates a novel surgical model to characterize in vivo signal propagation and subsequently identify insulating materials for use in implantable interface systems currently in development. Improved signal isolation through the utilization of these materials stands to greatly improve control fidelity of neuroprosthetic limbs.

The application of hyperbaric oxygen therapy in the management of compromised flaps.

INTRODUCTION: Hyperbaric oxygen (HBO2) therapy has been used to promote viability of compromised flaps despite a paucity of supportive clinical evidence. This study provides an in-depth characterization of hyperbaric medicine to promote flap survival and identifies treatment variables associated with positive clinical outcomes. METHODS: A retrospective review was conducted of patients who received HBO2 therapy for a failing or threatened post-reconstructive flap from 5/30/2008 through 4/30/2012. Medical records were reviewed to collect patient characteristics, hyperbaric oxygen therapy details, and clinical outcomes. Descriptive and comparative statistics were utilized. RESULTS: Ninety-one patients underwent HBO2 therapy during this time period, with 15 patients meeting the selection criteria. Flap survival was achieved in 11 patients (73.3%). Of those successfully treated, four (36.4%) healed completely, and seven (63.6%) demonstrated marked improvement. Patients who were treated successfully demonstrated an average improvement in flap area of 68.3%. Variables significantly associated with a favorable treatment outcome included a high percentage of treatment completion (p = 0.022) and high pretreatment transcutaneous oxygen measurements (p = 0.05). Smoking was a negative factor (p = 0.011). CONCLUSION: This study provides clinical data characterizing and supporting the application of hyperbaric medicine to aid in the viability of compromised flaps.

Electrically stimulated signals from a long-term Regenerative Peripheral Nerve Interface.

Despite modern technological advances, the most widely available prostheses provide little functional recovery beyond basic grasping. Although sophisticated upper extremity prostheses are available, optimal prosthetic interfaces which give patients high-fidelity control of these artificial limbs are limited. We have developed a novel Regenerative Peripheral Nerve Interface (RPNI), which consists of a unit of free muscle that has been neurotized by a transected peripheral nerve. In conjunction with a biocompatible electrode on the muscle surface, the RPNI facilitates signal transduction from a residual peripheral nerve to a neuroprosthetic limb. The purpose of this study was to explore signal quality and reliability in an RPNI following an extended period of implantation. Following a 14-month maturation period, electromyographic signal generation was evaluated via electrical stimulation of the innervating nerve. The long-term RPNI was viable and healthy, as demonstrated by evoked compound muscle action potentials as well as histological tissue analysis. Signals exceeding 4 mV were successfully acquired and amplitudes were consistent across multiple repetitions of applied stimuli. There were no evident signs of muscle denervation, significant scar tissue, or muscle necrosis. This study provides further evidence that after a maturation period exceeding 1 year, reliable and consistent signals can still be acquired from an RPNI.

Fatal upper gastrointestinal bleed arising from duodenal varices secondary to undiagnosed portal hypertension.

Duodenal varices are an unexpected source of upper gastrointestinal haemorrhage associated with high mortality. The prevalence of ectopic variceal bleeding accounts for 2-5% of all variceal bleeding; of this, only 17% occurs in the duodenum. Diagnosis is difficult, and insufficient evidence exists to demonstrate the best treatment option when haemorrhage occurs. We report the case of a 69-year-old man with a history of chronic alcoholism who presented to the emergency department (ED) with nausea, vomiting and several episodes of haematochezia. Diagnostic workup in the ED included CT with multiplanar reconstruction, which revealed a network of large tortuous blood vessels running near the second portion of the duodenum between the inferior vena cava and portal vein. The patient was emergently treated with endoscopic therapy and clipping of the vessel. This failed, and he was subsequently taken to the operating room for suture ligation of the bleeding duodenal varices.

Clinical factors associated with replantation after traumatic major upper extremity amputation.

BACKGROUND: Little knowledge exists concerning replantation following traumatic major upper extremity amputation. This study characterizes the injury patterns and outcomes of patients suffering major upper extremity amputation and ascertains clinical factors associated with the decision to attempt replantation. METHODS: A retrospective cohort study was conducted on patients treated at a Level I trauma center between June of 2000 and August of 2011. Patients who experienced traumatic upper extremity amputation at or proximal to the radiocarpal joint were included in the study. The subset of patients subsequently undergoing replantation was identified. Medical records were reviewed and bivariate analysis was performed to identify factors associated with attempted replantation and replant survival. RESULTS: Sixty-two patients were treated for traumatic upper extremity amputation and 20 patients underwent replantation. Injury factors associated with attempted replantation included a sharp/penetrating injury (p = 0.004), distal level of amputation (p = 0.017), Injury Severity Score less than 16 (p = 0.020), absence of avulsion (p = 0.002), absence of significant contamination (p ≤ 0.001), and lack of multilevel involvement (p = 0.007). Replantation exhibited a complete replant survival rate of 70 percent. An Injury Severity Score of 16 or more was associated with replant failure (p = 0.004). Patients who underwent replantation demonstrated increased rates of secondary surgical revisions (p ≤ 0.001) and complications (p = 0.023) and had a greater length of hospital stay (p = 0.024). CONCLUSIONS: Several injury characteristics are associated with the decision to attempt replantation of the major upper extremity. A high global injury severity (Injury Severity Score ≥ 16) is associated with replantation failure when attempted. Patients who undergo replantation demonstrate higher resource use, warranting further cost-analysis and outcomes investigation. CLINICAL QUESTION/LEVEL OF EVIDENCE: Risk, III.